The unifying focus of the proposed research is the study of human auditory cortex. The two specific areas of investigation will be: l) Cellular electrophysiology of human auditory cortex, 2) Feasibility studies of an auditory cortex neural prosthetic device concept. Cellular Electrophysiology of Human Auditory Cortex: The function of human auditory cortex has been, and continues to be, the subject of intensive research. Until recently, no method was available to investigate the electrophysiology of human auditory cortex at the cellular level. The candidate and his collaborators have developed a technique for obtaining simultaneous recordings from several groups of individual auditory cortex neurons in awake humans. Acute and chronic recordings are carried out in epilepsy surgery patients using a hybrid depth electrode with both research and clinical recording capabilities. Fundamental questions concerning human tonotopic organization and receptive field plasticity can now be addressed directly. Cortical Neural Prosthetic Device Feasibility: Cochlear implants have been remarkably successful in restoring hearing to deaf patients with residual cochlear nerve function. Patients without cochlear nerve function, however, cannot benefit from electrical stimulation of the cochlea. To treat such patients, brainstem cochlear nucleus implants have been developed to deliver electrical impulses directly to the central auditory system. Using methods developed to localize and place electrodes into auditory cortex, microstimulation experiments will be carried out to determine the feasibility of developing a cortical central auditory prosthetic device. Compared to the cochlear nucleus implants currently in use, auditory cortex implants have theoretical safety advantages as well as the potential for use in a wider range of hearing disorders. The unifying theme of this proposal is to study the physiologic properties of human auditory cortex using novel recording and microstimulation techniques. In addition to the potential direct benefits of better understanding the physiology of human hearing, and of laying the groundwork for the development of a useful neuralprosthetic device for deaf patients, there are long-term indirect benefits. The expertise developed during this project will facilitate the candidate's efforts to become an established independent investigator. In the future, similar methods could be applied to the study of other, non-auditory brain regions. The experience and skills gained during this project may also be applied to the future development of cortical neuralprosthetic devices in somatosensory, visual, or motor cortex-devices which could have profound impact on millions of disabled Americans.